This invention relates to new propylene/ethylene random copolymers with very high randomness. More particularly, the invention relates to propylene/ethylene random copolymers which are suitable as materials for the production of molded articles excellent in stiffness, heat resistance, transparency, etc.
Olefin polymers represented by polypropylene and polyethylene have been extensively used as a base resin in the field of various moldings, because of their good mechanical properties, good chemical resistance and very useful balance with economy. These olefin copolymers have been produced by polymerizing olefins using Ziegler-Natta catalyst system comprising a transition metal catalyst component having titanium trichloride, titanium tetrachloride or the mixture thereof supported on a support such as magnesium chloride, in combination with an organoaluminum compound.
In recent years, various processes of polymerizing olefins have been proposed using a metallocene catalyst system comprising an organic transition metal compound having specified organic radical different from an inorganic transition metal compound, what is called a metallocene compound in combination with an aluminoxane. The olefin copolymers produced using the metallocene catalyst system are generally those having narrow molecular weight distribution. In particular, where two or more olefins are copolymerized, comonomers are dispersed homogenously and copolymerized, thus producing more homogenous copolymers with high randomness as compared with those using Ziegler-Natta catalyst system. Further, choice of metallocene species can produce an isotactic polypropylene having high stereoregularity.
These propylene/ethylene random copolymers are compounded with various additives to form pellets and provided for the manufacture of various molded articles such as films, injection moldings, blow moldings, sheets, fibers, etc. For these molding materials, basic properties of propylene/ethylene copolymers are specified and the additives are selected in accordance with the intended object.
EP 0629631, JPA 7-149833 and JPA 8-73532 disclose the application to films of isotactic polypropylenes produced using a metallocene catalyst system. JPA 7-149833 and JPA 8-73532 disclose that propylene/ethylene random copolymers produced by copolymerizing propylene and ethylene using a metallocene catalyst system comprising a particular chiral metallocene compound are characterized by 13C-NMR spectroscopy and that propylene/ethylene random copolymers having the following characteristics exhibit a heat-sealing property which is one of performances required for film.
However, these publications give no reference to the randomness of the ethylene unit present in the polymer chain.
As one embodiment of polypropylene films, there are biaxially oriented multi-layer films produced generally by laminating a basic layer comprising a crystalline polypropylene film and a heat-seal layer being heat sealable at lower temperature, followed by biaxial orientation. JPA 8-238729 discloses a composite film using as a heat seal layer a propylene/1-butene random copolymer produced with a metallocene catalyst system. This copolymer has 1.0 to 1.5 of parameter B value indicating the randomness in chain distribution of comonomers in the polymer chain. Parameter B value indicating the randomness is represented by the following equation.
B=P12/(2P1xc2x7P2)
wherein P1 and P2 represent a first monomer content fraction and a second monomer content fraction, respectively, and P12 represents the proportion of (first monomer)xe2x80x94(second monomer) chain in the whole two molecule chains.
JPA 9-110934 (Japanese Patent Appln. 7-272428) filed by the present applicant discloses propylene/ethylene random copolymers produced by copolymerizing propylene and ethylene using an olefin polymerization catalyst comprising a single mixture system of a specific chiral metallocene compound and aluminoxane, and injection moldings and films comprising these copolymers as a base resin.
JPA-5-9225, JPA-5-9226 and JPA-5-32723 disclose polypropylene resins produced with the intention of improving the mechanical properties such as stiffness and heat resistance of moldings. These polypropylene resins contain propylene polymers having the temperature (T max) of above 117.0xc2x0 C. or 118.0xc2x0 C., which indicates a position of the main elution peak by a temperature fractionation method, and also contain a nucleating agent as a desired component.
JPA 7-10932 also discloses a polypropylene resin composition for injection molding which comprises a propylene polymer as a base resin into which a nucleating agent is incorporated. In this propylene polymer, the weight percent of the amount of the propylene polymer dissolved in o-dichlorobenzene between 120xc2x0 C. and 135xc2x0 C., based on the total weight of the propylene polymer is more than the value calculated from the equation: (40-15 logMFR)xc3x97100 wherein MFR represents a melt flow rate of propylene polymer.
WO 94/28219 discloses a composition for the formation of fibers wherein a low-melting homopolypropylene produced using a metallocene catalyst system is kneaded with a radical generating agent to lower a molecular weight of propylene.
As discussed above, different characteristics are required for propylene polymers, depending on the object of molding. Producing separately propylene polymers satisfying such respective characteristics complicates process step and process control, thus increasing the cost of production.
An object of the invention is to provide a propylene/ethylene random copolymer which is suitable as a base resin for molding materials applicable to a wide variety of molding fields.
Another object of the invention is to provide a molding material comprising a propylene/ethylene random copolymer as a main component, which is usable in a wide variety of molding fields.
A further object of the invention is to provide a biaxially oriented multi-layer polypropylene film with high transparency, which comprises a polypropylene film having excellent heat resistance and stiffness and very high transparency, and a heat-seal layer having excellent heat-sealing and anti-blocking properties.
A propylene/ethylene random copolymer of the present invention is characterized in that:
an ethylene content (Ew) is 0.1-10 wt %,
a relationship between an isolated ethylene content (E1) and the ethylene content (Ew) is represented by the following equation:
E1 greater than 0.85xe2x88x920.01Ew
2,1- and 1,3-propylene units present in a polymer chain are 0-1 mol %,
a weight average molecular weight (Mw) is in the range of 40,000-1,000,000, and
a ratio (Mw/Mn) of the weight average molecular weight (Mw) to a number average molecular weight (Mn) is in the range of 1.5-3.8.
The propylene/ethylene random copolymer can be produced by copolymerizing propylene and ethylene in the presence of a supported metallocene catalyst comprising a transition metal compound and aluminoxane or the reaction product thereof supported on a fine particle support and an organoaluminum compound.
The above-mentioned transition metal compound is represented by the following formula 
wherein M represents a transition metal selected from the group consisting of titanium, zirconium and hafnium; X and Y may be the same or different and each represents a hydrogen, a halogen or a hydrocarbyl radical; (C5H4xe2x88x92mR1m) and (C5H4xe2x88x92nR2n) represent a substituted cyclopentadienyl group in which m and n are an integer of 1-3; R1 and R2 may be the same or different and each represents a hydrocarbyl radical of 1 to 20 carbons or a silicone-containing hydrocarbyl radical, with the position of R1 and R2 on the cyclopentadienyl ring giving a configuration wherein any symmetry plane containing M each other is absent; and Q is a divalent hydrocarbyl radical, an unsubstituted silylene group and a hydrocarbyl-substituted silylene group. Preferably, at least one of R1 and R2 substitutes a carbon adjacent to a carbon attached to Q in the cyclopentadienyl ring.
The first embodiment of molding materials according to the present invention is a propylene composition comprising the propylene/ethylene random copolymer and a desired additive component.
The second embodiment of molding materials is a propylene/ethylene random copolymer composition comprising an xcex1-crystal nucleating agent in an amount of 0.0001-1 part by weight based on 100 parts by weight of the copolymer and a desired additive component.
The third embodiment of molding materials is a propylene/ethylene random copolymer composition comprising the propylene/ethylene random copolymer, a radical generator in an amount of 0.001-0.5 part by weight based on 100 parts by weight of the copolymer and a desired additive component. This composition is modified by melt kneading of the above individual components at a temperature of 150 to 300xc2x0 C.
The molded articles according to the present invention include films, sheets, injection moldings, extrusion moldings, blow moldings and fibers which are formed from the above first molding materials, the propylene compositions.
The films according to the present invention are those formed from the above first molding materials, the propylene compositions.
Another embodiment of the films according to the present invention is a composite film comprising a film layer formed from the above first molding materials, the propylene compositions and other polypropylene films.
A further embodiment of the films according to the present invention is a stretched, multi-layer polypropylene film having a heat-seal layer comprising a film layer formed from the above first molding materials on at least one surface of the basic layer comprising a crystalline polypropylene as a main component. This multi-layer polypropylene film is preferably biaxially oriented.
The first embodiment of the molded articles according to the present invention is injection moldings molded from the above first molding materials, the propylene compositions.
The second embodiment of the molded articles is injection moldings molded from the above second molding materials, the propylene/ethylene random copolymer compositions.